As a technique to enhance a magnet property of a rare earth permanent magnet containing neodymium (Nd), iron (Fe), and boron (B), there is a magnet in which Fe is substituted with Co (PTL 1). PTL 1 describes that a coercive force Hc, residual magnetic flux density Br, maximum energy product BHmax, and so on of permanent magnets in which Fe is substituted with other atoms were measured exhaustively, thereby showing enhancement of the magnetic property of the above-described permanent magnet.
Furthermore, PTL 2 discloses a rare earth sintered magnet that contains, by percent by weight: R (where R is at least one type of rare earth elements including Y and Nd accounts for 50 atom % or more of R): 25 to 35%; B: 0.8 to 1.5%; M (at least one type selected from Ti, Cr, Ga, Mn, Co, Ni, Cu, Zn, Nb, and Al) when necessary: 8% or less; and the remainder T (Fe or Fe and Co).
As another suggestion to enhance the magnetic property of the rare earth permanent magnet, there is a nanocomposite magnet having a two-phase composite structure in which a hard magnet phase of nanoparticles consisting of Nd, Fe, and B forms a core and a soft magnet phase of specified nanoparticles forms a shell. Regarding the above-mentioned nanocomposite magnet, particularly when the shell is formed by covering the core with a grain boundary composed of very fine particles of a soft magnetic substance whose particle size is 5 nm or less, a good exchange interaction occurs between the hard magnet phase and the soft magnet phase, that is, the core and the shell, thereby making it possible to enhance saturation magnetization.
PTL 3 discloses a nanocomposite magnet in which Nd2Fe14B compound particles form a core and Fe particles form a shell. The saturation magnetization of the nanocomposite magnet is further enhanced by using FeCo alloy nanoparticles which exhibit high saturation magnetization as a shell constituent. PTL 4 discloses a nanocomposite magnet in which a core of an NdFeB hard magnet phase is covered with a shell of an FeCo soft magnet phase.
PTL 5 discloses an anisotropy bulk nanocomposite rare earth permanent magnet regarding which a composition of a magnetically hard phase as defined by atom percentage is RxT100-x-yMy (where in this expression, R is selected from rare earths, yttrium, scandium, or a combination of these elements; T is selected from one or more types of transition metals; M is selected from elements of group IIIA, elements of group IVA, elements of group VA, or a combination of these elements; x is larger than a stoichiometric amount of R in a corresponding rare-earth transition-metal compound; and y is 0 to approximately 25) and at least one type of a magnetically-soft phase includes at least one type of a soft magnetic material containing Fe, Co, or N.
However, with the nanocomposite rare earth permanent magnet disclosed in PTL 5, a soft phase is formed by a metallurgical method. Accordingly, the particle size of particles which form the soft phase is large. So, there is a possibility that a sufficient exchange interaction may not be obtained. Furthermore, if reducing power is weak, alloy nanoparticles tend to easily become just an aggregate of single-layer nanoparticles and a desired nanocomposite structure cannot be obtained. Therefore, it is presumed that the magnetic property of the above-described nanocomposite rare earth permanent magnet may not be enhanced effectively.
NPL 1 discloses a method for manufacturing FeCo nanoparticles at a high temperature. However, a coercive force Hcj of the relevant Nd2Fe14B particles manufactured at a high temperature is not good.